1. Field of the Invention
The present invention relates to an improved amphibious marsh craft and its track system, and more particularly to an improved track system that maximizes buoyancy by eliminating bogie wheels while eliminating prior art "roller chain" and its lubrication and wear problems.
2. General Background of the Invention
Various types of amphibious marsh crafts are known in the art. One commonly known and cited is U.S. Pat. No. 2,546,523 issued Mar. 27, 1951 to Reynolds which discloses a marsh buggy vehicle comprising a pair of spaced, elongated pontoons disposed and secured in a parallel relationship, two endless chains passing about each pontoon over sprockets mounted on transverse, driven shafts. The chains were joined together transversely by slats which form the threads for the craft.
Another example of an amphibious marsh vehicle is shown in U.S. Pat. No. 3,842,785 issued Oct. 22, 1974 to Rivet. The apparatus described by Rivet included two pontoons, with two endless drive chains carried in channels disposed on top and bottom of the pontoons. The cleats attached to the chains have plastic blocks which are secured to the web of the cleats and bear against the top and bottom of the pontoons.
These and other similar vehicles have a number of operating problems, one of the most common of which is roller chain wear. In operation the chain is exposed to the mud, sand and water, and to prolong the chain life it is a common practice to lubricate the elements of the chain in places of connection. But any lubricant applied to a chain has a tendency to catch and collect dirt and sand, which causes rapid wear of the chain elements, particularly between the carrier roller and pin.
To solve this problem some inventors have come up with the idea of using rubber belts instead of metal chains, as for example in U.S. Pat. No. 3,217,687 issued Nov. 16, 1965 to Erkelson et al., which describes an amphibious vehicle having endless belts provided for operation mainly in water when the belts are substantially submerged.
But such vehicles face another problem when traveling on the ground, this problem being commonly known as "chain" or "track throw," which arises from the inability of many such designs to provide efficient means for securing a chain or a belt in its place over the driving sprockets or wheels.
Additionally, many "marsh buggies" have had the problem of "track sag," which further adds to the problem of track throw.
These problems have been known in the art for a long period of time and, to prevent rapid wear of the elements, a number of solutions have been suggested. In some cases special pads are attached to the sides of a chain in order to reduce friction and thus to eliminate the problem. While these and other solutions have proven to be satisfactory to some extent, they still have not provided full reliability.
In my prior U.S. Pat. No. 4,433,634, there is provided a tracked, amphibious vehicle with a track securement and guide means. The invention shown and described in the '634 patent was designed to prevent "track throw" or loss. The vehicle shown and described in the '634 patent includes two spaced, parallel pontoons joined by a centrally located operator's platform structure, with each pontoon having a moveable track for propulsion, with the track supported on its pontoon by fore and aft sprocket wheel sets and a series of larger bogie wheels at its bottom and smaller guide wheels at its top. Each track comprises a parallel set of rubber, continuous, endless belts joined together by a series of laterally disposed cleats with drive lugs, which lugs are engaged by the teeth of the sprocket wheels. For track securement in the first embodiment (FIG. 5) every fifth cleat includes an inwardly projecting, polyethylene T-hanger retainer which matingly fits and rides in a beam guide attached to the bottom of the pontoon and extends from the initial bottom bogie wheel to the entry of the aft, drive sprocket. In a second embodiment (note FIG. 6), the securing parts are reversed with the T-retainer element being a continuous beam fixed to the bottom of the pontoon and with the mating receptive elements being on the cleats of the track. For track guidance every cleat includes a pair of outwardly facing, inwardly directed, vertical guide members which face the inward or interior sides of the upper and lower bogie wheels to prevent, any lateral forces from moving the track off its pontoon. U.S. Pat. No. 4,433,634 is incorporated herein by reference.
One of the compromises that accompany the use of bogie wheels such as those shown and described in the '634 patent (see for example FIG. 3), is that of reduced pontoon area especially in the lower end portion of the pontoon where the bogie wheels must be located. This necessarily limits the amount of load that can be carried.
Another problem that has long plagued marsh vehicles is the need for endless drive chains that encircle each pontoon, engaging sprockets mounted on the transverse driven shafts. Though chain driven type amphibious marsh crafts have been in use for a number or years, the chain has always been a source of high maintenance, breakage, and down time. The endless roller chains have very small bearings that are quickly worn away by sand, grit, and soil. In some soil conditions, chain wear is much faster than in others. However, the problem of track chain wear has long plagued the art.